Abstract Islet1 (Isl1) is a transcription factor transiently expressed in a subset of heart and
limb progenitors. During studies of limb development, conditional Isl1 deletion produced
unexpected kidney abnormalities. Here, we studied the renal expression of Isl1 and whether
it has a role in kidney development. In situ hybridization revealed Isl1 expression in the
mesenchymal cells surrounding the base of the ureteric bud in mice. Conditional deletion of
Isl1 caused kidney agenesis or hypoplasia and hydroureter, a phenotype resembling human …